Crawling The Deep Web
A vast amount of Web pages lie in the deep or invisible Web. These pages are typically only accessible by submitting queries to a database, and regular crawlers are unable to find these pages if there are no links that point to them. Google's Sitemaps protocol and mod oai are intended to allow discovery of these deep-Web resources.
Deep Web crawling also multiplies the number of Web links to be crawled. Some crawlers only take some of the -shaped URLs. In some cases, such as the Googlebot, Web crawling is done on all text contained inside the hypertext content, tags, or text.
Strategic approaches may be taken to target deep-Web content. With a technique called screen scraping, specialized software may be customized to automatically and repeatedly query a given Web form with the intention of aggregating the resulting data. Such software can be used to span multiple Web forms across multiple Websites. Data extracted from the results of one Web form submission can be taken and applied as input to another Web form thus establishing continuity across the Deep Web in a way not possible with traditional web crawlers.
Read more about this topic: Web Crawler
Famous quotes containing the words crawling, deep and/or web:
“But see, amid the mimic rout
A crawling shape intrude!”
—Edgar Allan Poe (1809–1849)
“Come now, let us go and be dumb. Let us sit with our hands on our mouths, a long, austere, Pythagorean lustrum. Let us live in corners, and do chores, and suffer, and weep, and drudge, with eyes and hearts that love the Lord. Silence, seclusion, austerity, may pierce deep into the grandeur and secret of our being, and so diving, bring up out of secular darkness, the sublimities of the moral constitution.”
—Ralph Waldo Emerson (1803–1882)
“For us necessity is not as of old an image without us, with whom we can do warfare; it is a magic web woven through and through us, like that magnetic system of which modern science speaks, penetrating us with a network subtler than our subtlest nerves, yet bearing in it the central forces of the world.”
—Walter Pater (1839–1894)